Air diffusers for directing a throw of air from a heating and air conditioning system into a room are well known. When directing air through a drop ceiling, such as commonly used in office buildings, the function of the air diffuser is to distribute the air uniformly and to circulate the air in the room without producing uncomfortable drafts. It is therefore desirable to provide a ceiling air diffuser which directs the air initially in a substantially horizontal pattern extending along the underside of the ceiling toward one of the walls of the office, thus setting up a pattern of air circulation around the margins of the room.
An example of a linear air diffuser for a drop ceiling is shown in U.S. Pat. No. 3,406,623. In this type of linear air diffuser, a plenum chamber is positioned above the drop ceiling and air is discharged from the plenum chamber through a restricted throat formed by a pair of closely spaced, vertical walls. Air is discharged from this throat against a horizontal ledge located along the edge of an opening in the plane of the ceiling. The ledge directs the air through the opening in a direction in which the discharged air tends to flow horizontally along the surface of the ceiling. The amount of air discharged through the opening in the ceiling is limited by the width of the throat which is substantially narrower than the ceiling opening.